Variable transformers



R. A. UTTER 3,074,036 VARIABLE mmsmams Filed Aug. 22, 1960 United tates atent O f 3,074,036 VARIABLE TRANFORMERS Ross A. Utter, Des Plaines, IlL, assignor to Zenith Radio Corporation, a corporation of Delaware Filed Aug. 22, 1969, Ser. No. 51,172 1 Claim. (Cl. 336132) This invention relates to transformers and, more specifically, to variable transformers in which there are no moving electrical contacts or flexing lead connections.

It is well known that variations in the output voltage of a power transformer may be accomplished by providing the output winding with a series of taps for selective engagementwith an output terminal or brush. The switching between difierent output voltages which is inherent in such devices makes it difficult if not impossible to adapt such devices to precision applications; moreover, in applications in which it is necessary to change the Volt age under load conditions, unwanted arcing may result.

Other known variable output transformers operate on the principle of varying the amount of primary flux linking the secondary winding, but such devices either suffer from the disadvantage of requiring flexing lead wires or fail to maintain optimum power handling capacity for a given line voltage.

Another approach to variable output transformers involves the provision of additional secondary windings upon the transformer yoke for developing an opposing or bucking voltage which when connected into the circuit with the main secondary winding reduces the net voltage of the secondary circuit. This latter approach has inherent inefliciencies, among which is the need to draw additional primary current for the bucking coil.

Still another system for supplying a varying output voltage involves an autotransformer device wherein a current is passed through a winding on an iron core. A variable output voltage is taken across a portion of the windings by means of a sliding contact or brush moving across the turns of wire forming the primary winding. The autotransformer approach has the inherent problem of handling high instantaneous currents in individual turns of the primary winding when short-circuited by the brush in moving across the winding.

' It is a principal object of this invention to provide a new and improved variable transformer.

It is another object to provide a variable transformer in which there are no short-circuited turns.

Further, it is an object of this invention to provide a variable transformer without flexing lead wires.

It is a further object to provide a new and improved differential transformer with no moving electrical contacts or flexing Wires.

A differential transformer embodying the invention comprises a magnetic circuit including a ferromagnetic yoke member having a first portion joining a pair of opposed leg portions and means including a movable ferromagnetic bridge member in sliding contact with the leg portions for completing the magnetic circuit. There is a first multi-turn winding encompassing one of the leg portions and a second multi-turn winding encompassing the other of the leg portions, the first and second multi-turn windings each having separate output terminals to derive separate secondary voltages. Furthermore, there is a third winding encompassing the yoke member, spaced from the first and second windings and responsive to an 3,074,036 Patented Jan. 15, 19fi3 applied voltage to establish a predetermined flux in the magnetic circuit. Finally, means are provided for moving the bridge member in simultaneous oppositely oriented sliding contact with both of the leg portions in a direction generally parallel to the axes of the first and second windings to increase the number of turns of the first winding linked with the flux while decreasing the number of turns of the second Winding linked with the flux.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claim. The organization and manner of operation of the invention together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a cross-sectional view of a variable transformer embodying the invention;

FIGURE 2 is a cross-sectional view of another embodiment of the invention;

FIGURE 3 is a cross-sectional view of a third embodiment of the invention;

FIGURE 4 is a cross-sectional view of still another embodiment of the invention; and

FIGURE 5 is a cross-sectional view of still another embodiment of the invention.

In the embodiment of the invention shown in FIG- URE l, a laminated L-shaped yoke member 1 made oi iron or other ferromagnetic material is shown having two divergent legs 10 and 21. In the embodiment of FIG- URE 1, the two legs 1% and 21 diverge at approximately with respect to each other although the amount of divergence is primarily a mechanical consideration and is not critical. Bridge member 3, also an L-shaped laminated member of iron or other ferromagnetic material, has two leg portions 11, 24). Leg 2-0 is of such dimension that it snugly fits through aperture 22 and is in sliding contact with leg 10 across contact area 8. Leg 11 of bridge member 3 is in sliding contact with yoke leg 21 across contact area 4. A primary winding 5 encompasses a portion of leg 21 of yoke member 1 and has terminal connections brought out through case 27 to terminals 15, 16, which in turn are connected to an energizing voltage source 2%. A multi-turn secondary winding 6 encompasses a second portion of leg 21 of the yoke member, being wound in slots 12 on the yoke so that the winding turns are recessed in contact surface 4. Output leads from secondary winding 6 are brought out through case 27 and connected through terminals 2 9, 30 and in turn are connected across load 31. Means are provided for moving an extremity of bridge member 3, in sliding contact with second portion of leg 21 across contact area 4 in a direction generally parallel to axis 32 of the secondary winding. This driving means comprises a rack 23 afflxed to bridge member 3 and in driven relation to a pinion gear 24 mounted on a rotatable shaft 25. A hand-wheel 26 is fixed to shaft 25 to facilitate manual adjustment.

in operation, an alternating voltage is applied across input terminals 15, 16 of the primary winding 5 which establishes a primary flux in a path 9 through leg 21 of yoke 1, across contact area 4, through leg 11 and leg 20 or" bridge member 3, across contact area 8 and through leg of yoke 1. Secondary winding a encompasses a portion of this flux path and, for a given setting of the bridge member, a predetermined output voltage is produced across terminals 29, of the secondary winding. Rotation of hand-wheel 2c in a clockwise direction (as viewed in the drawing) causes pinion gear 24 to rotate clockwise and to drive rack 23 to the left. Bridge memher 3 affixed to the rack moves toward the left, in a direction generally parallel to axis 32 of the secondary windmg. Sliding contact 4 of course moves to the left and the number of turns of secondary Winding 6 encompassing primary flux path 9 is reduced and hence the voltage induced in the secondary Winding is reduced. Conversely, rotation of hand-wheel 26 in the counterclockwise direction causes bridge member 3 to move to the right, increasing the number of turns of the secondary winding encompassing the flux path and resulting in an increased voltage across terminals 29, 3h.

The embodiment of the invention shown in PlGURE has a magnetic circuit including a ferromagnetic yoke which is of a generally U-shaped laminated construction of iron or other ferromagnetic material having a pair of legs 41, 42 land a bight or connecting portion 43. The circuit also includes a laminated ferromagnetic or iron bridge member 44. A primary winding 46 encompasses the bight portion of the U-shaped yoke member and is responsive to an applied input alternating voltage to establish a predetermined flux in the magnetic circuit, as represented by path Multiple-turn secondary windings 47 and 48 encompass legs 41 and 4-2, respectively, of yoke member 40. Secondary windings 47 and 48 are each equipped with output terminals which allows them to be used separately or connected in parallel or in series as desired. Hand wheel 49 turns shaft 50 and pinion gear 51 which drives rack 52 and moves bridge member 44 in sliding contact with leg portions 41, 42 of yoke member 40. The direction of motion of bridge'me'mber 44 is generally parallel to the axes of secondary windings 47 and 48, as represented by broken lines 53, 54. The portion of the secondary windings on the interfaces of the legs 41, 42 are recessed in two series of notches 55 and 56, permitting bridge member 44 to slide back and forth across contact areas 57, 5% while maintaining a relatively constant cross-sectional area of contact.

In operation, rotation of the hand wheel in a counterclockwise direction causes the pinion gear to rotate in a counter-clockwise direction driving the rack and bridge member to the right. Thus, the fiux path 45 is extended to the right and more turns of the secondary windings encompass the fiux path. This results in an increase in voltage output across the output terminals of secondary coils 47, 4%.

In the embodiment shown in FIGURE 3, the yoke member is composed of a series of laminations having a first leg 61 and a second leg as of a curved shape. A bridge member 63 is in pivotal contact across area 64- of leg 61 and in sliding contact across area 65 with curved leg 62. A primary winding s7 encompasses part of the first leg of the yoke and is responsive to an applied alternating voltage to establish a predetermined flux in the magnetic circuit along a path as extending through the first leg 61 of'yoke member 66', through the pivotal contact area 64, through the bridge member 63-, across sliding contact area 65 and through a portion of the curved leg 62. A secondary winding ca encompasses a portion of the curved leg and has its windings on the interface recessed in notches 6%.

Means are also provided for pivoting bridge member 63 about pivotal contact area at. Such means comprise handwheel 70 which rotates pinion gear 71, drives gear 72 and pivots bridge member 63 about pivotal contact area 64. The extremity of the bridge member 63 in sliding contact with the curved leg 62 across contact area 65 slides in a direction generally parallel to the curved axis of secondary winding 68- which varies the number of turns of the secondary winding encompass-ing the flux established by the primary winding 67 and results in a variation of the output voltage across terminals 73, '74.

Another embodiment of the invention is shown in FIGURE 4, which illustrates a differential transformer. Laminated yoke 75 has a first portion 76 joining a pair of opposed leg portions 77 and 78. A first multi-turn secondary winding 53 encompasses leg 77 of yoke member 75 and a second multi-turn secondary winding $4 encompasses leg 78 of yoke member 75. The portions of the multi-turn windings 83 and 84 on the side of the yoke 75 in contact with bridge member 79 are recessed in slots 84' and 85. A movable laminated ferromagnetic bridge member 7?, in sliding con-tact with legs 77 and78, completes the magnetic circuit. Means including handwheel 88, pinion 100, and rack 101 are provided for moving bridge member 79 in simultaneous oppositely oriented sliding contact with opposed leg portions 77 and 78 in a direction generally parallel to the axes of windings 83 and 34; in other words, movement of bridge member 7 in a direction generally parallel to the axis of the first and second windings increases the number of turns of one winding which are actively linked with the primary flux whiie decreasing the number of turns of the other winding linked with the flux in the magnetic circuit. A third, or primary, winding 8-9 spaced from windings 83, 84 encompasses a portion of yoke member 75, and establishes a predetermined flux as shown by line 82 in the magnetic circuit. Clockwise rotation of the handwheel 88 drives the bridge member in an upward direction and causes the magnetic path to be varied. The first multiturn winding 33 has fewer turns encompassing the flux of the magnetic circuit and its output voltage is reduced while at the same time the second multi-turn secondary winding 84 has the number of turns encompassing the magnetic flux increased and its output voltage is increased. Hence, the device operates as a differential transformer in that one control causes opposite variations in the output of two sets of terminals.

FIGURE 5 illustrates another differential transformer embodying the invention. In FIGURE 5, the bridge member 90 is mounted at its mid point 91 to a rotatable shaft or pivot. Operation of the hand wheel and gear train simultaneously move the extremities of bridge 90 in simultaneous oppositely oriented sliding contact with legs S 2, 93 of the yoke member in directions generally parallel to the axes of the two secondary windings 96, 97. Rotation of the handwheel in the clockwise direction alters the magnetic flux path 95 and reduces the number of turns of winding 96 that are coupled to the primary flux while increasing the number of turns of Winding 97 linking the primary flux. The result is that the voltage output across winding 96 is reduced while at the same time that across winding 97 is increased.

From the foregoing description of the invention, it is apparent that the invention provides new and improved variable transformers with no flexing leads, no shortcircuited turns, and no sliding electrical contacts. The invention is also applicable to differential transformers for providing a pair of correlated output voltages concurrently variable in opposite senses.

While particular embodiments of the invention have been shown and. described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broad er aspects, and, therefore, the aim in the appended claim is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

A differential transformer comprising: a magnetic circuit including a ferromagnetic yoke member having a first portion joining a pair of opposed leg portions and means including a movable ferromagnetic bridge member in sliding contact with said leg portions for completing said magnetic circuit; a first multi-turn winding encompassing one of said leg portions; a second multi-turn Winding encompassing the other of said leg portions, said first and second multi-turn windings each having separate output terminals to derive separate secondary voltages; at third winding encompassingsaid yoke member, spaced from said first and second windings and responsive to an applied voltage to establish a predetermined flux in said magnetic circuit; and means for moving said bridge member in simultaneous oppositely oriented sliding contact with both of said leg portions in a direction generally parallel to the axes of said first and second windings to increase the number of turns of said first winding linked with said flux while decreasing the number of turns of said second 5' winding linked with said flux.

References Qited in the file of this patent UNITED STATES PATENTS 693,841 Cutcheon Feb. 25, 1902 

